1. Field of the Invention
The present invention relates generally to a device for ruling off the length of a needle or cannula, and more specifically to devices for ruling that portion of a needle or cannula which is to be inserted into a patient such that the portion to be inserted into the patient can be gauged and marked with a needle stop prior to insertion.
2. Description of the Related Art
Needles are commonly employed to obtain biopsy specimens for laboratory evaluation. This entails a surgical procedure which requires that the surgeon know precisely the depth to which the needle is inserted in the patient's tissue to be sure that a proper specimen is obtained. Typically, spaced markings are provided along the surface of the needle to indicate the depth of penetration of its tip. A depth stop may be employed to limit penetration of the needle to the desired depth.
The practice of providing spaced markings along the surface of the needle is attended by significant disadvantages. A primary disadvantage is the difficulty of reading such markings. The limited surface area of a typical needle necessarily imposes constraints on the size of the markings which may be etched thereupon. Small markings are difficult for a surgeon to read with the naked eye. The low contrast between the needle surface and the marking exaggerates this problem. The problem is made worse if lighting conditions are poor, or if the needle is held in a position which causes light to be reflected from it.
Another common practice involving such needles is that of providing a protective covering, or shield, over the needle and needle tip to protect against needle damage, accidental sticking of the user's fingers, and puncture of the package within which the needle is shipped. A shield is placed over each individual needle for shipping, handling, and storage purposes, and is removed and discarded prior to use of the needle.
Some protective coverings were designed to perform a dual function: to seal the needle portion of an instrument and gauge the depth of penetration of the needle. For example, U.S. Pat. No. 4,022,191 to Jamshidi discloses a sleeve guard made of a frangible material. The outer circumference of the shank of the sleeve guard has a plurality of spaced apart circumferential grooves disposed at spaced intervals along the length of the sleeve guard. The grooves are formed in such a way that the depth of the grooves is sufficient to permit the shank to break upon flexure. The breakage forms an open ended sleeve which exposes a predetermined length of the needle and serves as a stop for the needle when it enters the body of a patient.
Some of the clear disadvantages of that sleeve guard are the need to complicate the manufacturing process by having to cut the grooves, the necessity to break the shank to expose a part of the needle for insertion, the limited number of the available needle lengths which can be exposed depending on the number and a spacing of the grooves.
Another solution, disclosed in U.S. Pat. No. 5,217,438 to Davis et al., provides a stop for a biopsy needle or the like, comprising a continuous wire spring formed in a series of adjacent coils. The internal diameter of each of the coils in the unstressed condition is selected to be less than the outer diameter of the shaft on the needle. The spring has two end portions that can move toward each other and expand the coils radially. The spring with expanded coils may be moved along the shaft of the needle to a particular location. Releasing the two end portions causes the spring to grip the surface of the needle shaft, therefore, providing a depth gauge for the portion of the needle which will be inserted into a patient.
The disadvantage of the spring device of the Davis et al. is the necessity to have a separate rule to measure the insertion depth of the needle. Additionally, the stress exerted on the tubular shaft of the needle by the spring can damage or break the needle.
Therefore, a need remains for a simple, easy to use, and clearly visible means by which a surgeon, or operator may rule the desired penetration depth of a needle prior to insertion of the needle in a patient's body. Coincidentally, an opportunity exists for further advantageous use of the protective shield within which needles and needle tips are enclosed for shipping and storing.